In order to recover natural resources from subterranean formations it is often necessary to perform tasks related to exploration, monitoring, maintenance and construction in remote locations that are either difficult or impractical for personnel to reach directly. For example, boreholes may be drilled tens of thousands of meters into the earth, and in the case of offshore drilling the borehole may be thousands of meters under water. One of the technical challenges to performing tasks in such remote locations is providing power to equipment. It is known to power downhole and undersea equipment via either stored energy or wireline connection to the surface. However, both of these techniques have disadvantages. For example, a wireline connection to the surface limits that distance at which the equipment can operate relative to the energy source, and may require a relatively significant portion of the limited volume of a borehole; and in many situations running a wireline is not even possible. Using stored energy avoids some of the disadvantages of a wireline connection to the surface, but relatively little energy can be stored in comparison to requirements because of size limitations. For example, the available volume in a borehole environment is relatively small for a battery having a relatively large storage capacity. Further, both wireline connection to the surface and stored energy techniques require the presence of operators, e.g., a surface vessel to either provide the wireline energy or recharge the energy storage means. Therefore, it would be beneficial to be able to generate electrical power in a remote location, e.g., in relatively close proximity to a well tool which consumes the electrical power without the need for physical connection with the surface or retrieval for recharge.
Various techniques are known for converting the kinetic energy associated with flowing fluid into electrical energy. U.S. Pat. No. 6,504,258 describes a downhole power generator which produces electrical power from vibrations in response to fluid flow. One limitation of this design is that the flow rate is greatly affected by the energy harvesting function. It is accordingly an object of the present invention to provide a method and an apparatus to harvest kinetic energy from fluid flow with minimal interference with fluid flow.